<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Tree Structure Visualization</title>
<style>
  .tree ul {
    list-style-type: none;
    padding-left: 20px;
    position: relative;
  }
  .tree li {
    margin: 5px 0;
  }
  .tree li::before {
    content: '';
    position: absolute;
    top: 0;
    left: -20px;
    width: 15px;
    height: 1px;
    background-color: #ccc;
  }
  .tree li::after {
    content: '';
    position: absolute;
    top: 12px;
    left: -20px;
    width: 20px;
    height: 0;
    border-top: 1px solid #ccc;
  }
</style>
</head>
<body>

<div class="tree">
  <ul>
    <li>Node 1
      <ul>
        <li>Node 1.1</li>
        <li>Node 1.2</li>
      </ul>
    </li>
    <li>Node 2
      <ul>
        <li>Node 2.1</li>
      </ul>
    </li>
  </ul>
</div>

</body>
</html>